Metals, metal salts, and metal complexes, deposited on chemically inert, high surface area carriers such as alumina and silica, are well known catalysts in organic chemistry. Rhodium is a metal often used in catalytic hydrogenation and use of rhodium compounds to activate carbon monoxide in its reactions with organic substrates is also well known; see, U.S. Pat. No. 3,527,809 and G. W. Parshall in "Homogeneous Catalysis", Wiley, New York, 1980, p. 85.
Hydroformylation, the addition of hydrogen and carbon monoxide to an olefin to provide an aldehyde, can be catalyzed by rhodium complexed with carbon monoxide and phosphine ligands; see, for example, U.S. Pat. Nos. 4,363,764 and 4,288,380. In U.S. Pat. No. 3,821,311, complex rhodium-containing catalysts have the general formula [(XRR.sup.1 R.sup.2).sub.m Rh(CO).sub.n Y.sub.q ].sub.r where m and n may be 0, 1, 2, 3, 4; q is 0, 1 or 3; and r is 1 or 2. X represents P, As or Sb and R, R.sup.1, and R.sup.2 are alkyl or aryl groups. Y represents hydrogen or electronegative substituents which are anionic when in the free state, i.e. substituents which are formally capable of undergoing nucleophilic substitution reactions, such as halogen, hydroxyl, alkoxyl or acylate, in that they are proton acceptors.
The background art has also taught the deposition of catalysts on inert supports or carriers wherein the carriers do not participate in the catalyzed reaction. Furthermore, the carriers, typically alumina or silica, are generally considered to be polymers comprised of monomeric, repeating, interconnected units, e.g. Al.sub.2 O.sub.3 or SiO.sub.2, respectively. Thus, a single crystal of silica can be considered to be one giant molecule.
Use of certain complex ions or clusters as catalysts is known in the art. These clusters are referred to as heteropolyanions or Keggin ions. They are discrete, charged molecular entities as contrasted with, for example, silica, and have the general formula X.sup.+n M.sub.12 O.sub.40 .sup.-(8-n) where M is molybdenum or tungsten and X is a metallic or metalloid element capable of forming an XO.sub.4.sup.-(8-n) oxyanion. The range of X, having formal oxidation number n, is quite large and includes Al, As, B, Co, Cu, Fe, P, Si and Zn. Substitution of some of the Mo or W atoms by other metallic elements, such as vanadium, also leads to clusters in which the basic Keggin ion structure is maintained. One-electron reduction of the X.sup.+n M.sub.12 O.sub.40.sup.-(8-n) ions by suitable chemical reagents such as NaBH.sub.4, sodium amalgam, hydrazine, etc. or by electrochemical means produces the X.sup.+n M.sub.12 O.sub.40.sup.-(9-n) analogs in which the basic metal oxide cluster structure is also retained. The Keggin ion compounds are reviewed in "Heteropoly and Isopoly Oxymetallates"by M. T. Pope, Springer-Verlag, New York, 1983, pp. 23-27 and pp. 125-127.
Use of mixtures of rhodium and/or platinum with tungsten oxide (WO.sub.3) to hydrogenate carbon monoxide to methane is disclosed in U.S. Pat. No. 3,787,468. In these catalysts, the metal oxide serves as an unreactive carrier for the metallic catalyst.
Molecular organometallic compounds, such as those containing the anion Rh(CO).sub.2 Cl.sub.2.sup.-, are disclosed by D. E. Hendricksen, C. D. Neyer, and R. Eisenberg, Inorg. Chem., 16, 970 (1977) as catalysts in the oxidation of carbon monoxide by nitric oxide according to the equation EQU 2 NO+CO.fwdarw.CO.sub.2 +N.sub.2 O
Schrock and Osborn, J. Am. Chem. Soc., 93, 2397, (1971) especially p. 2401, have prepared salts of (Ph.sub.3 P).sub.2 Rh(CO).sub.3 by CO displacement of organic ligands such as cyclooctadiene, bicycloheptadiene and acetone from, e.g., (Ph.sub.3 P).sub.3 Rh(cyclooctadiene).sup.+ ; counterions used are ClO.sub.4.sup.- and Ph.sub.4 B.sup.-. Simple addition of CO is not suggested.
U.S. Pat. No. 4,196,136 has described two rhodium-containing oxymetallates EQU [(CH.sub.3).sub.3 NH].sub.4 [(C.sub.7 H.sub.8).sub.2 RhSnPW.sub.11 O.sub.39 ] EQU [(CH.sub.3).sub.3 NH].sub.4 [(Ph.sub.3 P).sub.2 RhSnPW.sub.11 O.sub.39 ]
where C.sub.7 H.sub.8 is bicyclo[2.2.1]heptadiene. In these trimethylammonium salts, the oxymetallate cage is of the general Keggin type but with one of the tungsten atoms replaced by tin. The (C.sub.7 H.sub.8).sub.2 Rh and (Ph.sub.3 P).sub.2 Rh moieties are connected to the cage by rhodium-tin bonds. These compounds can be distinguished from those of the present invention, which contain neither tin nor Rh-Sn linkages, and thus are fundamentally different.